Allylation of Quinones with Allyltin Reagents

The marked similarity between this structure and that of cyclohexyllithium hexamer6 suggests that the metal-hydrogen interactions have little effect on the stereochemistry of these two derivatives, even though Li-H interactions may be present in the cyclohexyl derivative. The average Li-C distance in a series of organolithium compounds is 2.27 8, (Table SII124) and the corresponding average of all Li-Si distances in trimethylsilyllithium is 2.68 A. Subtracting the covalent radius of carbon from the average Li-C distance gives an effective radius for lithium of 1.50 A, whereas from the trimethylsilyl derivative we obtain 1.5 1 A. Considering the crudeness of the approximation this suggests that the "effective bonding radius" for lithium in multicentered bonds is 1.5 A, a value somewhat greater than the radius of lithium observed in Liz (1.34 A); this result is in keeping with the weaker nature of the multicentered interaction. It appears likely that other silyllithium compounds will have structures similar to that of trimethylsilyllithium in the solid state and in solution and that in the germanium analogues complex structures of a similar nature with Li-Ge distances on the order of 2.7 8, will obtain. Further work is necessary in the area of the structures of electron-deficient organolithium, silyllithium, and germyllithium compounds to determine the validity of the suggestions proposed, but they do provide a basis from which future studies may be started.